bug#21598: 24.5; Auto-revert-mode loads images as text

[Matthias Redies <rediesmatthias@yahoo.de>]

description:
This is how I reproduce the Bug:
1. open image C-x C-f and select "output.png". This will display the 
image as an image as it should.
2. change Image using an external program. This causes the
auto-revert-mode to reload the image(good), but as a text, although my
default (as in 1.) is to open the picture as an image

This forces me to redo C-x C-f, which makes auto-revert-mode pointless.



In GNU Emacs 24.5.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.16.6)
of 2015-09-14 on buildvm-10.phx2.fedoraproject.org
Windowing system distributor `Fedora Project


Copy and paste whole report:

Date: Thu, 01 Oct 2015 17:15:22 +0200
Message-ID: <8737xumxh1.fsf@linux.fritz.box>


description:
This is how I reproduce the Bug:
1. open image C-x C-f and select "output.png". This will display the 
image as an image as it should.
2. change Image using an external program. This causes the
auto-revert-mode to reload the image(good), but as a text, although my
default (as in 1.) is to open the picture as an image

This forces me to redo C-x C-f, which makes auto-revert-mode pointless.



In GNU Emacs 24.5.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.16.6)
  of 2015-09-14 on buildvm-10.phx2.fedoraproject.org
Windowing system distributor `Fedora Project', version 11.0.11702000
System Description:    Fedora release 22 (Twenty Two)

Configured using:
  `configure --build=x86_64-redhat-linux-gnu
  --host=x86_64-redhat-linux-gnu --program-prefix=
  --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
  --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
  --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
  --libexecdir=/usr/libexec --localstatedir=/var
  --sharedstatedir=/var/lib --mandir=/usr/share/man
  --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
  --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
  --with-gpm=no build_alias=x86_64-redhat-linux-gnu
  host_alias=x86_64-redhat-linux-gnu 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
  -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
  -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4
  -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
  -m64 -mtune=generic' LDFLAGS=-Wl,-z,relro'

Important settings:
   value of $LANG: de_DE.utf8
   value of $XMODIFIERS: @im=none
   locale-coding-system: utf-8-unix

Major mode: Image[png]

Minor modes in effect:
   global-auto-revert-mode: t
   shell-dirtrack-mode: t
   tooltip-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Recent messages:
Loading 
/usr/share/emacs/site-lisp/site-start.d/desktop-entry-mode-init.el 
(source)...done
Finding all versions of R on your system...
Sorry, no version of R could be found on your system.
For information about GNU Emacs and the GNU system, type C-h C-a.
scroll-up-command: End of buffer
call-interactively: End of buffer
C-c C-f is undefined
Making completion list... [2 times]
Type C-c C-c to view the image as text.
Reverting buffer `output.png'.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message cl-macs rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils vc-git image-mode help-mode autorevert filenotify
ido ess-toolbar ess-mouse mouseme thingatpt browse-url ess-menu ess-swv
ess-noweb ess-noweb-font-lock-mode ess-bugs-l essd-els ess-sas-d
ess-sas-l ess-sas-a shell pcomplete ess-sta-d ess-sta-l cc-vars cc-defs
make-regexp ess-sp6-d ess-sp3-d ess-julia julia-mode ert find-func ewoc
debug ess-r-d ess-r-completion compile ess-tracebug format-spec ess-roxy
advice hideshow ess-help ess-developer eldoc help-fns ess-s-l ess
ess-inf comint ansi-color ring ess-mode ess-noweb-mode ess-utils cl gv
cl-loaddefs cl-lib ess-custom executable easymenu ess-compat ess-site
autumn-light-theme time-date tooltip electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment lisp-mode prog-mode register
page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core frame cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese hebrew
greek romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dbusbind
gfilenotify dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 124278 7973)
  (symbols 48 24280 0)
  (miscs 40 52 112)
  (strings 32 32508 4413)
  (string-bytes 1 892807)
  (vectors 16 15689)
  (vector-slots 8 459570 5130)
  (floats 8 124 266)
  (intervals 56 262 0)
  (buffers 960 15)
  (heap 1024 53411 1010))